feat: Add file selector support and enhance game data directory management

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

packages/wolf_3d_flutter/lib/managers/game_data_directory_persistence_io.dart

@@ -22,7 +22,7 @@ class DefaultGameDataDirectoryPersistence {
       return _resolvedPath!;
     }
 
-    _resolvedPath = '$platformConfigDir/data_source.json';
+    _resolvedPath = '$platformConfigDir/settings.json';
     return _resolvedPath!;
   }
 
@@ -61,18 +61,36 @@ class DefaultGameDataDirectoryPersistence {
     try {
       final normalized = directoryPath?.trim();
       final file = File(filePath);
+      Map<String, Object?> existingPayload = <String, Object?>{};
+
+      if (await file.exists()) {
+        try {
+          final String raw = await file.readAsString();
+          final Object? decoded = jsonDecode(raw);
+          if (decoded is Map<String, Object?>) {
+            existingPayload = decoded;
+          }
+        } catch (_) {
+          // Ignore malformed existing content.
+        }
+      }
 
       await file.parent.create(recursive: true);
       if (normalized == null || normalized.isEmpty) {
-        if (await file.exists()) {
-          await file.delete();
+        existingPayload.remove('dataDirectory');
+        if (existingPayload.isEmpty) {
+          if (await file.exists()) {
+            await file.delete();
+          }
+          return;
         }
+        final payload = jsonEncode(existingPayload);
+        await file.writeAsString(payload, flush: true);
         return;
       }
 
-      final payload = jsonEncode(<String, Object>{
-        'dataDirectory': normalized,
-      });
+      existingPayload['dataDirectory'] = normalized;
+      final payload = jsonEncode(existingPayload);
       await file.writeAsString(payload, flush: true);
     } catch (_) {
       // Best-effort only.